1. Field of the Invention
The present invention relates to a method and apparatus for detecting the condition of the flow of liquid metal in or from a teeming vessel and more particularly to a method and apparatus for detecting the presence of an undesirable condition in the flow of liquid metal in or from the teeming vessel.
2. Description of the Prior Art
Liquid metal and in particular liquid steel is drained from a draining or teeming vessel, normally a ladle, into one or more molds usually through an intermediate or receiving vessel, normally a tundish. In this process, a controlled flow of liquid metal passes from the ladle, normally through a nozzle and valve in the bottom of the ladle, into a ceramic tube and then into a receiving vessel, normally a tundish. A tundish is a refractory-lined vessel equipped with one or multiple outlets through which the metal flows into the mold(s).
As the teeming ladle approaches empty, slag and oxidation products which float on-top of the liquid steel in the ladle, can be entrained within the teeming flow and transferred to the tundish. Usually, as the teeming ladle is approaching empty, the surface of the liquid steel in the tundish is observed visually and when slag is seen to be entering the receiving vessel, the valve in the teeming ladle is closed in order to reduce the contamination of the metal in the tundish or mold with slag and oxidation products. Alternatively, an electromagnetic coil may be employed to assist in the detection of the presence of slag or non-metallics in the teeming flow and to automatically signal for valve closure. Typically, this coil surrounds the nozzle of the teeming ladle and senses variations of the electromagnetic field produced by the excitation of the coil related to changes in non-metallic content of the flow.
It is well known that flow from a teeming ladle induces vibration of the ladle itself, the ceramic tube which is attached to the ladle, and the tundish. In particular, vibration of the tube can be substantial. Attempts have been made to sense this vibration manually.
The prior art does not address the following problems:
Visual Slag Detection PA0 Electromagnetic Slag Detection PA0 Prior Art Vibration Sensing
Visibility of slag entrainment within the tundish is poor. Therefore, the ability of the ladle teeming operator to see slag is difficult and the consistency of ladle flow closure is poor. Early ladle closure results in lost metal yield and late ladle closure results in slag contamination of the liquid steel in the tundish. As multiple ladles are poured into one tundish, slag build-up occurs and the problem of visibility is compounded. A significant problem associated with visual slag detection is that slag is not seen until it is already present in the tundish.
The sensor coil is located in the ladle and therefore, is highly susceptible to thermal and physical damage. The ladle must be specifically adapted to accept the coil and as each ladle arrives at the teeming position, a cable connection must be performed. Steel penetration in the nozzle block can damage the coil or impede its operation. A teeming ladle must be removed from the operational cycle to replace a damaged or non-performing coil. In this situation, slag is not detected until it is present within the nozzle block of the teeming ladle and already flowing toward the tundish.
Manual vibration sensing is inconsistent and operator dependent. The human threshold to sense and discriminate change in vibration is limited. As with the above two methodologies, slag is detected when it is present and flowing through the tube attached to the ladle.